1. Field of the Invention
The present invention relates to an ultrasonic diagnostic equipment for use in the fields of medical care, etc., and more particularly to video technology utilizing a nonlinear phenomenon.
2. Description of the Related Art
An ultrasonic diagnostic equipment is a medical image equipment with which the tomographic image of a soft tissue in a living body is noninvasively obtained from the surface of the body by the ultrasonic pulse echo method. As compared with other medical image equipment, the ultrasonic diagnostic equipment has such merits as being small-sized and inexpensive, affording a high safety without exposure to X-rays etc., and being capable of blood flow imaging, and it is extensively utilized for the heart, the abdomen and the urinary organs and in obstetrics and gynecology, etc.
In the ultrasonic image diagnostic equipment, bio-information can be imaged by various imaging methods. The contrast echo method, for example, gives an ultrasonic contrast medium made of microbubbles or the likes, into the blood vessel of a patient, thereby to attain the enhancement of an ultrasonic scattering echo. In such an imaging method, it has hitherto been an important problem to extract an echo signal component to-be-imaged at a high S/N ratio from a received signal. Therefore, various contrivances have been made in the respective imaging methods.
Concretely, in second harmonic imaging, the band of a second harmonic wave to-be-imaged is determined by that of a fundamental wave. Accordingly, the bandwidth of the second harmonic wave is controlled by adjusting the fundamental wave band, so as to obtain a signal suitable for the imaging. By way of example, in order to broaden the second harmonic wave onto a lower frequency side, the fundamental wave may, in principle, be broadened onto the lower frequency side. Besides, in case of broadening the second harmonic wave onto a higher frequency side, the fundamental wave may be broadened onto the higher frequency side.
In actuality, however, the band of the fundamental wave as can be broadened onto the lower frequency side is limited by a probe band as shown in FIG. 1A. Besides, in a case where the second harmonic wave has been broadened onto the higher frequency band, the bands of the fundamental wave and the second harmonic wave overlap each other in the received signal as shown in FIG. 1A, so that separation into the respective bands is sometimes difficult.
Besides, in the contrast echo, when a band intermediate between the fundamental wave and the second harmonic wave is imaged, the contrast between the tissue and the contrast medium can be heightened.
However, it is difficult to completely remove the fundamental wave and the second harmonic wave at all times, and in the case where the intermediate band has been imaged, it is sometimes impossible to offer appropriate bio-information. By way of example, in a case where the vicinity of a 1.5f0 band is imaged as shown in FIG. 1B, it can occur that parts of both the waves enter the band to-be-imaged, and that a tissue exhibiting a high echo is imaged together in the contrasting mode, to make the judgment of contrast difficult.